U.S. patent number 6,865,174 [Application Number 09/601,886] was granted by the patent office on 2005-03-08 for code division multiple access communication system.
This patent grant is currently assigned to Kazuo Tsubouchi. Invention is credited to Kazuya Masu, Tomohiko Shibata, Kazuo Tsubouchi.
United States Patent |
6,865,174 |
Tsubouchi , et al. |
March 8, 2005 |
Code division multiple access communication system
Abstract
In a code division multiple communication system which prevents
the dropout of a whole packet and does not require the generation
of a carrier from a received signal, under bad communication path,
by generating an orthogonal code with chip synchronization from a
correlation peak of a synchronization code sequence output from a
surface acoustic wave matched filter, a preamble division of a
spectrum spread signal is composed of plural synchronization burst.
Each synchronization burst is composed of a synchronization packet
division having the Barker code of 11 chips and a dummy division.
The period of one synchronization burst (T.sub.burst) is set
equally to the period of one symbol in a data division
(T.sub.symbol) which is modulated by the orthogonal sequential code
of 64 chips. When the correlation peak of at least one from among
plural synchronization code sequences is detected, the orthogonal
code can be generated in accordance with the start timing of the
first symbol in the data division.
Inventors: |
Tsubouchi; Kazuo (Sendai-shi,
Miyagi 982-0222, JP), Masu; Kazuya (Sendai,
JP), Shibata; Tomohiko (Kasugai, JP) |
Assignee: |
Tsubouchi; Kazuo
(JP)
|
Family
ID: |
18410933 |
Appl.
No.: |
09/601,886 |
Filed: |
October 27, 2000 |
PCT
Filed: |
December 09, 1999 |
PCT No.: |
PCT/JP99/06907 |
371(c)(1),(2),(4) Date: |
October 27, 2000 |
PCT
Pub. No.: |
WO00/35110 |
PCT
Pub. Date: |
June 15, 2000 |
Foreign Application Priority Data
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Dec 9, 1998 [JP] |
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10-350502 |
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Current U.S.
Class: |
370/342; 370/335;
370/515; 375/E1.002; 375/E1.017; 375/E1.003 |
Current CPC
Class: |
H04B
1/70712 (20130101); H04B 1/707 (20130101); H04B
1/7075 (20130101); H04B 1/7093 (20130101) |
Current International
Class: |
H04B
1/707 (20060101); H04B 007/216 () |
Field of
Search: |
;370/509,512,514,343,328,203,208,441,431,329,335,342,350,503,515
;375/140,142,143,145,149,150,151,152,153,354,363-368 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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5680414 |
October 1997 |
Durrant et al. |
6160838 |
December 2000 |
Shinohara et al. |
6275123 |
August 2001 |
Tanaka et al. |
6366603 |
April 2002 |
Uchida et al. |
|
Foreign Patent Documents
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|
|
|
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0 797 315 |
|
Sep 1997 |
|
EP |
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3-167930 |
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Jul 1991 |
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JP |
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6-204971 |
|
Jul 1994 |
|
JP |
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7-16442 |
|
Mar 1995 |
|
JP |
|
8-139637 |
|
May 1996 |
|
JP |
|
9-261121 |
|
Oct 1997 |
|
JP |
|
10-294715 |
|
Nov 1998 |
|
JP |
|
Other References
Milstein, Laurence B., et al., "Rapid Acquistion for Direct
Sequence Spread-Spectrum Communications Using Parallel SAW
Convolvers", IEEE Transactions on Communications, vol. COM-33, No.
7, Jul. 1985, pp. 593-600. .
Engineering Science Society, "Proceedings of the 1996 Engineering
Sciences Society Conference of IEICE", Sep. 18-21, 1996, Kanazawa
University, cover page plus pp. 362-363..
|
Primary Examiner: Patel; Ajit
Attorney, Agent or Firm: Parkhurst & Wendel, L.L.P.
Claims
What is claimed is:
1. A code division multiple access communication system in which in
a transmitter, a code division multiple signal, composed of a data
division obtained by multiplying a baseband data and an orthogonal
code and a preamble division including synchronization code
sequences to attain the chip synchronization of the orthogonal code
in a receiver, is modulated with a carrier having a given center
frequency and transmitted, and in the receiver, a correlation peak
is detected from among the synchronization code sequences in the
preamble division by a surface acoustic wave matched filter and the
baseband data in the data division is demodulated by the orthogonal
code generated on the detection timing, wherein the period of the
synchronization burst, in the preamble division (T.sub.burst),
which is composed of a synchronization packet division having at
least one synchronization code sequence and a dummy division next
to the packet division, is set equally to the period of one symbol
in the data division (T.sub.symbol).
2. A code division multiple access communication system as defined
in claim 1, wherein the preamble division has plural
synchronization bursts.
3. A code division multiple access communication system as defined
in claim 2, wherein the repeated number of the plural
synchronization bursts in the preamble division is set to 5-15.
4. A code division multiple access communication system as defined
in claim 3, wherein the repeated number of the plural
synchronization bursts in the preamble division is set to 6-12.
5. A code division multiple access communication system as defined
in claim 1, wherein the chip rate of the synchronization code
sequence in the preamble division is higher than the chip rate of
the orthogonal code in the data division.
6. A code division multiple access communication system as defined
in claim 5, wherein the chip rate of the synchronization code
sequence in the preamble division is integral times of not less
than two as high as the chip rate of the orthogonal code in the
data division.
7. A code division multiple access communication system as defined
in claim 1, wherein the chip length of the orthogonal code in the
data division is set to be 64 chips.
8. A code division multiple access communication system in which in
a transmitter, a code division multiple access signal, composed of
a data division obtained by multiplying a baseband data and an
orthogonal code and a preamble division including synchronization
code sequences to attain the chip synchronization of the orthogonal
code in a receiver, is modulated with a carrier having a given
center frequency and transmitted, and in the receiver, a
correlation peak is detected from among the synchronization code
sequences in the preamble division by a surface acoustic wave
matched filter and the baseband data in the data division is
demodulated by the orthogonal code generated on the detection
timing, wherein the preamble division has plural synchronization
code sequences, and the surface acoustic wave matched filter
detects the correlation peak of at least one from among the plural
synchronization code sequences and generates the orthogonal code on
the detection timing of the correlation peak; and wherein the
preamble division is composed of N.sub.burst -multiple repeated
synchronization bursts, each burst being composed of a
synchronization packet division having at least one synchronization
code sequence and a dummy division next to the packet division, and
the period of one synchronization burst (T.sub.burst) is set to be
integral times as long as the period of one symbol in the data
division (T.sub.symbol).
9. A code division multiple access communication system as defined
in claim 8, wherein the surface acoustic wave matched filter has an
aluminum nitride film as its component.
10. A code division multiple communication access system as defined
in claim 9, wherein the period of the burst in the preamble
division (T.sub.burst) is set equally to the period of one symbol
in the data division (T.sub.symbol).
11. A code division multiple communication access system as defined
in claim 9, wherein the multiple repeated number N.sub.burst of the
plural bursts constituting the preamble division is set to
5-15.
12. A code division multiple communication access system as defined
in claim 11, wherein the multiple repeated number N.sub.burst of
the plural bursts constituting the preamble division is set to
6-12.
13. A code division multiple access communication system as defined
in claim 9, wherein the chip rate of the synchronization code
sequence in the preamble division is higher than the chip rate of
the orthogonal code in the data division.
14. A code division multiple access communication system as defined
in claim 13, wherein the chip rate of the synchronization code
sequence in the preamble division is integral times of not less
than two as high as the chip rate of the orthogonal code in the
data division.
15. A code division multiple access communication system as defined
in claim 9, wherein the chip length of the orthogonal code in the
data division is set to 64 chips.
16. A code division multiple access communication system in which
in a transmitter, a code division multiple signal, composed of a
data division obtained by multiplying a baseband data and an
orthogonal code and a preamble division including synchronization
code sequences to attain the chip synchronization of the orthogonal
code in a receiver, is modulated with a carrier having a given
center frequency and transmitted, and in the receiver, a
correlation peak is detected from among the synchronization code
sequences in the preamble division by Ma surface acoustic wave
matched filter and the baseband data in the data division is
demodulated by the orthogonal code generated on the detection
timing, wherein in the receiver, the orthogonal code which is
generated on the detection timing of the ion peak in the surface
acoustic wave matched filter is multiplied by the received code
division multiple signal to generate a narrow-band modulation
signal, and the generated narrow-band modulation signal is
demodulated by a carrier generated from a local oscillator provided
in the receiver to reproduce the original baseband data; and
wherein the preamble division is composed of multiple repeated
synchronization bursts, each burst being composed of a
synchronizaton packet division having at least one synchronization
code sequence and a dummy division next to the packet division, and
the period of one synchronization burst (T.sub.burst) is set to be
integral times as long as the period of the symbol in the data
division (T.sub.symbol).
17. A code division multiple access communication system as defined
in claim 16, wherein the local oscillator provided in the receiver
generates the carrier having the frequency equal to the center
frequency of the carrier generated in the transmitter, and the
generated carrier from the local oscillator is multiplied by the
narrow-band modulation signal to demodulate the baseband data.
18. A code division multiple access communication system as defined
in claim 16, wherein the local oscillator provided in the receiver
generates a carrier having a different frequency from the center
frequency of the carrier generated in the transmitter, the
generated carrier from the local oscillator being multiplied by the
narrow-band modulation signal to generate a narrow-band modulation
signal having their differential frequency, and the narrow-band
modulation signal having the differential frequency is demodulated
to demodulate the baseband data.
19. A code division multiple access communication system as defined
in claim 16, wherein the period of one synchronization burst
(T.sub.burst) is set equally to the period of one symbol in the
data division (T.sub.symbol).
20. A code division multiple access communication system as defined
in claim 19, wherein the repeated number of the plural
synchronization bursts in the preamble division is set to 5-15.
21. A code division multiple access communication system as defined
in claim 20, wherein the repeated number of the plural
synchronization bursts in the preamble division is set to 6-12.
22. A code division multiple access communication system as defined
in claim 16, wherein the chip rate of the synchronization sequence
in the preamble division is set to be higher than the chip rate of
the orthogonal code in the data division.
23. A code division multiple access communication system as defined
in claim 22, wherein the chip rate of the synchronization sequence
in the preamble division is set to be integral times of not less
than two as high as the chip rate of the orthogonal code in the
data division.
24. A code division multiple access communication system as defined
in claim 16, wherein the chip length of the orthogonal code in the
data division is set to 64.
Description
TECHNICAL FIELD
This invention relates to Spread Spectrum Communication System,
particular to Code Division Multiple Access Communication System
which is capable of performing a high speed synchronization.
BACKGROUND ART
In advanced information community, communication technique,
particularly, wireless communication technique is required to be
developed. One of the wireless communication technique is that a
base station (herein, called as a "transmitting station") provided
in a cell (called as a "local area cell") having a radius of
several hundred meter and plural mobile stations (called as a
"receiving station") moving in the local area cell wirelessly
communicate one another at the same time. In such a wireless
communication, plural channels which do not interfere with one
another must be installed. Therefore, as a multiple access system,
Frequency Division Multiple Access (FDMA), Time Division Multiple
Access (TDMA), Code Division Multiple Access (CDMA) or the like are
suggested. This invention belongs to'the Code Division Multiple
Access (CDMA) in these multiple access systems.
The CDMA is also called "Spread Spectrum Communication (SSC) system
because its frequency spectrum is spread by modulating baseband
data with a high speed digital code. The SS-CDMA has excellent
characteristics of fading-resistance, multipass-resistance and
interference-resistance, and has distribution exchange function and
position-determining function.
In this invention, a "down link" means a two-way transmission from
a base station localized almost at the center of a cell to plural
mobile stations in the cell. Hereinafter, a "transmitting station"
means the base station, and a "receiving station" means the mobile
station. In the down link of such a SS-CDMA (communication from the
transmitting station to the receiving station), baseband data are
multiplied by a carrier having a given center frequency in the
transmitting station to generate a primary modulation signal, by
which a spread code (pseudo-noise (PN) code) is multiplied to
transmit a secondary modulation signal having a spread spectrum. In
the receiving station, the same spread code and the same carrier as
in the transmitting station are generated, and multiplied by the
received signal to demodulate the original baseband data.
As a spread code in such a SS-CDMA communication system, an
orthogonal code is employed to identify many channels and, for
example, an orthogonal m-sequence code, an orthogonal Walsh code,
an orthogonal Gold code or the like may be exemplified. In
employing such an orthogonal code, the timing of the generation of
a given orthogonal code in a receiving station is required to be
synchronized with that in a transmitting station. This code
synchronization is called as a "chip synchronization".
Conventionally, in order to attain the chip synchronization, a
digital sliding correlation apparatus or a digital matched filter
is suggested.
The digital sliding correlation apparatus circulates the orthogonal
code at a higher speed than a received signal, and attains the chip
synchronization by a detector having a DLL (Delay Lock Loop).
However, it is disadvantage that the digital sliding correlation
apparatus becomes unstable in its operation due to the balance of
the correlation apparatus and requires long time in synchronization
acquisition because it has to circulate the code by maximum one
period.
Moreover, the digital matched filter detects the correlation peak
between a known orthogonal code and a received signal by
correlation-integrating both of them using a shift resistor, and
thereby, attains synchronization acquisition. Although the digital
matched filter can attain the synchronization at a higher speed
than the above digital sliding correlation apparatus, it may make
the timing of the correlation peak ambiguous. Moreover, in the
digital matched filter, as the number of the chips in the
orthogonal code per period increases, the bits in the shift
resistor increase, which results in the deterioration of the
economical efficiency thereof.
The digital matched filter using a silicon integrated circuit
technique generally operates in a baseband frequency, so that it
can not operate when it includes a carrier frequency. Therefore,
the received signal has to be input into the digital matched filter
after synchronous detection, etc. Generally, a secondary modulated
signal by a PN code has a spread spectrum, and has much difficulty
in the synchronous detection due to its small C/N ratio. In
principle, if a silicon integrated circuit using a microfabrication
technique of 0.2-0.13 .mu.m which is under development is employed,
the digital matched filter which operates at around 100 Hz can be
obtained. However, it is difficult to use the digital matched
filter for the receiver of a mobile machine requiring a low
electric power consumption because the silicon integrated circuit
has a large-scale circuit which means that an electric power
consumption is larger than at least 1 watt.
Moreover, it is disadvantage that the digital sliding correlation
apparatus and the digital matched filter have large electric power
consumption at stand-by state.
To solve the above problems, the present inventors suggest the
following code division multiple access communication system.
First, in a transmitter, a code division multiple signal which is
composed of a data division obtained by multiplying an orthogonal
code by a baseband and a preamble division to synchronize the
orthogonal code in a receiver is transmitted. Second, in the
receiver, the correlation peak is detected from the synchronized
code sequence in the preamble division by an surface acoustic wave
matched filter. At last, the orthogonal code is generated based on
the detection timing, and the received baseband data in the data
division is demodulated by the orthogonal code. Such a code
division multiple access communication system is described in for
example, Kokai Publication 9-261121(JP A 09-261121). Hereinafter,
the surface acoustic wave matched filter is called as a "SAW MF".
The "SAW MF" is abbreviated from the wording "Surface Acoustic Wave
Matched Filter".
The above-mentioned code division multiple access communication
system can synchronize the orthogonal code at a high speed.
Moreover, the surface acoustic wave matched filter is a passive
device, and has small electric power consumption, so that it can
essentially provide a receiving station having a small stand-by
electric power. Furthermore, since the surface acoustic wave
matched filter can correlate the code sequence of surface acoustic
wave matched filter with a code division multiple signal including
a carrier, it can correlate in a GHz band or RF band if it can made
of a suitable material for such bands. Therefore, since a received
signal in a RF band is directly input and correlated in the surface
acoustic wave matched filter, a pretreatment such as a down
converting is not advantageously required. As described later, a
SAW MF having an "aluminum nitride/sapphire" structure including an
aluminum nitride film is suitable for the SAW MF which can operate
in the GHz band.
In the conventional code division multiple access communication
system described in the above Kokai Publication 9-261121(JP A
09-261121), the preamble division is composed of a packet division
for synchronization having a Barker code of 11 chips as a code
sequence for synchronization and a dummy division of 5 chips next
to packet division for the synchronization, and the data division
is composed of n-sequential symbols of 1024 chips demodulated by
the orthogonal code. As mentioned above, in the conventional code
division multiple access communication system, there is the
preamble division in the receiver in order to generate the
synchronized orthogonal code with the chips in the data division of
the received code division multiple signal. However, the code
division multiple signal has only one code sequence for
synchronization at the front of one packet, so that the packet can
not be received entirely if the code sequence for synchronization
is not detected. Since there are large influences resulted from
various noises, multipass and cross talk between the adjacent cells
in wireless communication, the correlation peak of the code
sequence for synchronization can not be detected in good condition
if the preamble division has only one code sequence for
synchronization.
Moreover, in the conventional code division multiple access
communication system, the receiver generates the carrier which is
synchronized with the carrier of the code division multiple access
signal made from correlation peaks, i.e. output signal from the
surface acoustic wave matched filter, and combines the generated
carrier with the orthogonal code generated as mentioned above, and
demodulates the baseband data by multiplying the combined signal by
the received signal. The synchronized carrier with received carrier
in phase and frequency can be reproduced, in the period when the
correlation peak of the surface acoustic wave matched filter
appears. However, the communication circuit is required to be
devised to reproduce the carriers in the short period when the
correlation peak appears. Therefore, the circuit structure using a
simple method is desired.
It is a first object of the present invention to provide a code
division multiple access communication system which can attain the
chip synchronization in the code sequence for synchronization
precisely at a high speed even under a bad communication
environment, and thus, can remove the disadvantage of being
incapable of receiving the packet entirely.
It is a second object of the present invention to provide a code
division multiple access communication system which can demodulate
the baseband data precisely from the correlation peak of the
surface acoustic wave matched filter without the carrier
synchronized to the received signal, in addition to realizing the
first object.
This invention relates to a code division multiple access
communication system in which in a transmitter, a code division
multiple access signal, composed of a data division obtained by
multiplying a baseband data and an orthogonal code and a preamble
division including synchronization code sequences to attain the
chip synchronization of the orthogonal code in a receiver, is
modulated with a carrier having a given center frequency and
transmitted, and in the receiver, a correlation peak is detected,
from among the synchronization code sequences in the preamble
division by a surface acoustic wave matched filter and the baseband
data in the data division is demodulated by the orthogonal code
generated on the detection timing, wherein the preamble division
has plural synchronization code sequences, and the surface acoustic
wave matched filter detects the correlation peak of at least one
from among the plural synchronization code sequences and generates
the orthogonal code on the detection timing of the correlation
peak.
According to the code division multiple access communication system
of the present invention, the orthogonal code with the chip
synchronization can be generated if at least one of the plural
synchronization code sequence in the preamble division of the
transmitted signal can be detected by the surface acoustic wave
matched filter, which prevents the dropout of the whole packet.
As mentioned above, even if the preamble division has the plural
synchronization code sequences, the surface acoustic wave matched
filter can not always detect the correlation peaks of all the
synchronization code sequences. Thus, even if all the same
synchronization code sequences are employed, the timing of the
generation of the orthogonal code can not be estimated from the
detected correlation peaks. That is, if the preamble division has
10 synchronization code sequences for example, the surface acoustic
wave matched filter detect the correlation peaks from all the 10
synchronization code sequences at every detection thereof in an
idealistic condition. If only 9 synchronization code sequences are
detected due to the deterioration of the communication path,
generally, the starting time of the first symbol in the data
division can not be estimated from the correlation peaks of these 9
synchronization code sequences. To solve such a problem, it is
preferable to realize the synchronization code sequence
corresponding to the correlation peak by changing the construction
of the plural synchronization code sequences, but it results in the
complication of the construction of the transmitter or the
receiver.
In this invention, for ironing out this problem, it is preferable
that in a code division multiple access communication system in
which in a transmitter, a code division multiple access signal,
composed of a data division obtained by multiplying a baseband data
and an orthogonal code and a preamble division including
synchronization code sequences to attain the chip synchronization
of the orthogonal code in a receiver, is modulated with a carrier
having a given center frequency and transmitted, and in the
receiver, a correlation peak is detected from among the
synchronization code sequences in the preamble division by a
surface acoustic wave matched filter and the baseband data in the
data division is demodulated by the orthogonal code generated on
the detection timing, the period of the synchronization burst in
the preamble division (T.sub.burst) which is composed of a
synchronization packet division having at least one synchronization
code sequence and a dummy division next to the packet division, is
set equally to the integral multiples of the period of one symbol
in the data division (T.sub.symbol). In particular, it is most
preferable that T.sub.burst is equal to T.sub.symbol in the data
division.
According to the preferred code division multiple access
communication system, in the case that the preamble division has 10
synchronization code sequences having the same structure, for
example, if at least one correlation peak from among the
synchronization code sequences is detected, the orthogonal code can
be generated, in accordance with the start timing of the first
symbol in the data division.
Moreover, in this case, the orthogonal code can be generated on the
timing of the first detection of the correlation peak from the
synchronization code sequences in the preamble division, and the
operation of the orthogonal code generating circuit can be reset at
every detection of the correlation peaks as described later in an
embodiment. Since the latter case can generate the orthogonal code
on the timing much near the start timing of the data division, it
may attain the chip synchronization more precisely.
Moreover, the present invention to realize the second object as
mentioned above relates to a code division multiple access
communication system in which in a transmitter, a code division
multiple access signal, composed of a data division obtained by
multiplying a baseband data and an orthogonal code and a preamble
division including synchronization code sequences to attain the
chip synchronization of the orthogonal code in a receiver, is
modulated with a carrier having a given center frequency and
transmitted, and in the receiver, a correlation peak is detected
from among the synchronization code sequences in the preamble
division by a surface acoustic wave matched filter and the baseband
data in the data division is demodulated by the orthogonal code
generated on the detection timing, wherein in the receiver, the
orthogonal code which is generated on the detection timing of the
correlation peak in the surface acoustic wave matched filter is
multiplied by the received code division multiple signal to
generate a narrow-band modulation signal, and the generated
narrow-band modulation signal is demodulated by a carrier generated
from a local oscillator provided in the receiver to reproduce the
original baseband data.
In a preferred embodiment of the code division multiple access
communication system according to the present invention, the
carrier having the frequency equal to the center frequency of the
carrier generated in the transmitter is generated, and is
multiplied by the narrow-band modulation signal to demodulate the
baseband data.
Moreover, the carrier having a different frequency from the center
frequency of the carrier generated in the transmitter is generated,
and the narrow-band modulation signal having their differential
frequency is generated by multiplying the generated carrier and the
narrow-band modulation signal. Then, the narrow-band modulation
signal having their differential frequency is demodulated and
thereby, the baseband data is demodulated. This system is called a
"Heterodyne system".
In both cases, normal demodulation system may be employed in
reproducing the baseband data by demodulating the narrow-band
modulation signal.
Furthermore, in the present invention, it is ascertained that when
the repeated number N.sub.burst in the plural bursts constituting
the preamble division is set to 5-15, particularly 6-12, the
probability of the dropout of the whole packet due to not attaining
the chip synchronization is much less than that of the conventional
code division multiple communication access system.
In this invention, it is preferable that the chip rate of the
synchronization code sequence in the preamble division is higher
than the chip rate of the orthogonal code in the data division,
particularly, integral times of not less than two as high as the
chip rate of the orthogonal code in the data division. In this
case, since the correlation peak output from the surface acoustic
wave-matched filter is sharper in terms of time, the generation
timing of the orthogonal code can be defined more precisely.
As mentioned above, as the synchronization code sequence in the
preamble division, the Barker code of 11 chips, the M-sequential
code or the like may be employed, and as the orthogonal code in the
data division, the orthogonal m-sequential code, the orthogonal
Walsh code, the orthogonal Gold code or the like may be
employed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view showing entirely the construction of
the code division multiple access communication system of the
present invention,
FIG. 2 is a diagrammatic view showing an embodiment of the
construction of a code division multiple access communication
system in the code division multiple communication system of the
present invention,
FIG. 3 is a block diagram showing the construction of a base
station in the code division multiple access communication system
of the present invention,
FIG. 4 is a diagrammatic view showing a transmission signal from
the base station,
FIG. 5 is a block diagram showing the construction of a mobile
station in the code division multiple access communication system
of the present invention,
FIGS. 6A and 6B are diagrammatic views showing a spectrum spread
signal and a narrow-band modulated signal, respectively,
FIG. 7 is a block diagram showing the construction of another
mobile station in the code division multiple access communication
system of the present invention,
FIG. 8 is a block diagram showing the construction of still another
mobile station in the code division multiple access communication
system of the present invention, and
FIGS. 9A and 9B are diagrammatic views showing an extracting
operation of the output of a surface acoustic wave-matched
filter.
BEST MODE FOR CARRYING OUT THE PRESENT INVENTION
The explanation of the present invention referring to the attaching
drawings will be preceded by the definitions of the technical terms
in this specification.
Code Division Multiple Signal Packet
A packet composed of one preamble division provided at the head
thereof and a data division having plural symbols next to the
preamble division.
Packet Period (T.sub.packet)
A period composed of the preamble division and the data division
Data rate D [bps(bit per second)].
A bit number per second of baseband data composed of binary signal
[1,0].
Symbol Period (T.sub.symbol)
A period of the symbol in the data division.
Synchronization Burst
A signal section composed of a synchronization packet division
having at least one synchronization code sequence and a dummy
division next to the synchronization packet division.
Synchronous Burst Period (T.sub.burst)
A period of the synchronization burst.
Chip Length N [Chip]
In a SS system or a CDMA system, a PN code is multiplied and
secondarily modulated. The PN code is composed of given repeated
[1] and [0] codes. The number of the [1] and [0] codes is a "chip
length". Generally, if an orthogonal code of N chips is employed, a
N channel-communication can be carried out when the orthogonal code
or chip is synchronized.
Chip Rate R.sub.chip [cps (Chip Per Second)]
A chip rate is a transmission rate of a chip constituting a
synchronization code sequence and an orthogonal code. The chip rate
of the synchronization code sequence in the preamble division is
called as a "R.sub.pre ", and the chip rate of the orthogonal code
in the data division is called as a "R.sub.data ". In the data
division, the relation of R.sub.data /N=D is satisfied.
FIG. 1 diagrammatically shows the construction of the cell-network
using the code division multiple access communication system of the
present invention. Base stations 2a and 2b are provided in for
example, local area cells 1a and 1b having a radius of about 150 m,
and are connected to a control station 3 via for example, optical
fibers. Plural mobile stations 4a, 4b . . . can move in the local
cells 1a and 1b freely, and the base stations 2a and 2b detect
constantly which mobile station moves to the local area cell to
which the base stations belongs. Each of mobile stations 4a, 4b . .
. communicates with the base stations 2a and 2b. The communication
for the base station from the mobile station is called as a "up
link", and the communication for the mobile station from the base
station is called as a "down link". In the down link, the base
station transmits signals to the mobile station in the same cell at
the same timing, and the mobile station selectively demodulates the
signals for itself from among the transmitted signals. As mentioned
above, this invention relates to the down link technique. For
enhancing the usability of the cell-network, it is important to set
as many channels as possible in one cell. In this invention, for
realizing this object, the baseband data are demodulated by the
orthogonal code having a chip length N.
Generally, since in the down link, it is easy to transmit signals
for a mobile station from a base station, the packet construction
of the present invention can be easily employed for the down link.
In the up link for a base station from a mobile station, even if
the mobile stations transmits signals at the same timing, the
timings of the signals which reach the base station from the mobile
stations does not coincide with one another. However, if the
signals from every mobile station can be transmitted to the base
station at the same timing by some kind of method, the packet
construction of the present invention can be applied for the up
link.
FIG. 2 is a diagrammatic view showing the construction of a code
division multiple access signal packet in the code division
multiple access communication system of the present invention. The
code division multiple signal packet has a preamble division
including plural synchronization code sequences to perform the chip
synchronization and a data division including the baseband data
demodulated by an orthogonal code. The preamble division has plural
repeated synchronization burst which has synchronization packet
division including the synchronization code sequences and dummy
division next to the synchronization packet division.
For the synchronization packet division in the synchronization
burst division, the Barker code of 11 chip is transmitted in the
after-mentioned example. No signal may be transmitted for the dummy
division. In the above transmission, since no electric power is
transmitted for the dummy division, the integral electric power in
the whole packet can be advantageously repressed. In the following
embodiment, for repressing the integral electric power of the whole
packet and simplifying the packet construction, no signal is
transmitted to the dummy division. In the case of transmitting no
signal in the dummy division, the SAW MF does not output the
correlation peak, so that it does not influence the operation as
described later. Signals of code "1" or "0" may be transmitted in
the dummy division in sequence. Moreover, a signal of the code by
which the SAW MF in the receiver does not output the correlation
peak may be transmitted to the dummy division.
The synchronization code sequences which are repeated plural times
in the preamble division are Pseudo Random Noise Codes, which may
be composed of m-sequential codes, Barker codes, Gold codes or the
like, for example. In this embodiment, the Barker code of 1 chips
having the code construction of .left brkt-top.11100010010.right
brkt-bot. is used. The data division is composed of the baseband
data modulated by the orthogonal code, which may be composed of the
orthogonal m-sequential code, the orthogonal Gold code, the
orthogonal Walsh code or the like. The channel number is determined
by the chip length N of the orthogonal code, and in this
embodiment, the orthogonal m-sequential code of 64 chips is
employed. Although the orthogonal m-sequential code of 64 chips
gives 63 channels actually, for convenience of explanation, it
gives 64 channels.
As mentioned above, the synchronization code sequences in the
preamble division are composed of the Barker codes of 11 chips.
Then, when the repeated number is set to 5-15, particularly, 6-12,
the chip synchronization can be attained precisely, and in this
embodiment, the repeated number is set to 10.
It is ascertained that the above repeated number enables the chip
synchronization to be achieved in bad communication path.
The number of the symbol in the data division may be determined
freely if the protocol restriction is not considered, but in a real
case, the symbol number is set to 500-1000, in consideration of the
stability of a quartz oscillator and the Doppler shift due to the
movement of the mobile station. The reason is that even if the
generation timing of the orthogonal code is detected precisely and
thereby, the orthogonal code is generated, for example, the chip
rate of the orthogonal code to be generated in a receiver is
different from that of the received signal because the chip rate is
generated in the receiver independently. Even if the mobile station
remains stationary, the chip rate of the orthogonal code to be
generated in the receiver is different from that of the received
signal by several ppm to 10 ppm. Therefore, if extremely long data
are transmitted, the chip synchronization can not be achieved in
both the front and rear of the data division at the same time. Even
if the chip rate can be reproduced precisely in the receiver, it is
shifted due to the Doppler shift thereof when the mobile station is
moved. In the embodiment, when the difference between the chip rate
of the received signal and the chip rate to be generated in the
receiver was about 5-10 ppm, the data error due to the chip
synchronization was not considerable substantially in the
transmission of the packet of 500-1000 symbols.
As described later, in the case of transmitting the code division
multiple access signal packet shown in FIG. 2 practically, the
packet is multiplied by the carrier having a center frequency of
f.sub.0. The carrier center frequency f.sub.0 is set to 2.484 MHz
in consideration of the rule of Radio Law, and the band width is
set to the range of 26 MHz-width. In this case, the rule of RCR
STD-33 is considered. In view of the rule, the chip rate of the
code division multiple access signal packet (R.sub.chip) is
determined. In this embodiment, the chip rate of the
synchronization code sequence in the preamble division (R.sub.pre)
is set to 22 cps, and the chip rate of the orthogonal code in the
data division (R.sub.data) is set to 11 Mcps, which is half as
large as the chip rate R.sub.chip. As mentioned above, since the
chip length is set to 64 chips, the data rate D of the data
division is set to about 171 kbps from the equation R.sub.data
/N=D. As is apparent from the equation, as the chip length N is
increased, the chip rate R.sub.data is decreased, and as the chip
length N is decreased, the chip rate R.sub.data is increased.
For attaining the chip synchronization more precisely, it is
desired that the chip rate of the synchronization code sequence in
the preamble division (R.sub.pre) is larger than the chip rate of
the orthogonal code in the data division (R.sub.data). The reason
will be described hereinafter. In the correlation peak output from
the SAW MF, the envelope curve has a triangular wave-like shape in
the wave-profile with time. The time-period of the triangular wave
is the reciprocal number of the chip rate R.sub.pre. When the chip
rate R.sub.pre is set to 22 Mcps, the time-period is set to about
45 nsec. Since the generation timing of the orthogonal code is
detected by taking advantage of the triangular wave-profile, the
finite time-period of 45 nsec generates an error on the generation
timing of the orthogonal code. As the period of the orthogonal code
per chip is longer, the finite time-period of 45 nsec does not
influence the generation timing. Therefore, in the case that the
chip rate of the synchronization code sequence in the preamble
division (R.sub.pre) is larger than the chip rate of the orthogonal
code in the data division (R.sub.data), the chip synchronization
can be attained precisely.
Although the ratio of the chip rate R.sub.pre to the chip rate
R.sub.data is freely selected in principle, it is preferably set to
an integral number for designing and fabricating the communication
circuit easily.
In this embodiment, since the synchronization code sequence in the
preamble division is composed of the Barker code of 11 chips, the
period of the synchronization packet division is set to 500 nsec
from "(1/22 Mcps).times.11 chips". On the other hand, since in the
data division, the orthogonal m-sequential code is employed, the
period of one symbol (T.sub.symbol) is set to about 5.8 .mu.sec
from "(1/11 Mcps).times.64 chips". This invention is also
characterized in that the period of the synchronization burst in
the preamble division (T.sub.burst) is integral times as long as
the period of the symbol in the data division (T.sub.symbol).
However, in this embodiment, the T.sub.burst is set to be equal to
the T.sub.symbol, and the period of the dummy division is
determined so as to satisfy the condition. As mentioned above,
since the T.sub.symbol is equal to the T.sub.burst, T.sub.burst is
set to about 5.8 .mu.sec. The period of the synchronization packet
division is set to 500 nsec(=0.5 .mu.sec), the dummy period in the
synchronization packet division is set to "about 5.8 .mu.sec-0.5
.mu.sec=about 5.3 .mu.sec".
FIG. 3 is a block diagram showing the construction of base stations
(transmitting stations) 2a and 2b, which is similar to a
conventional one. That is, a baseband data to be transmitted from
the baseband data-generating circuit 11 is supplied to a first
multiplier 12, and then, the Barker code sequence of 11 chips and
the orthogonal m-sequential code of 64 chips which are output from
a spread signal-generating circuit 13 at a given timing are
supplied to the multiplier 12, to generate the code division
multiple access signal packet shown in FIG. 2. The thus generated
code division multiple access signal packet is supplied to a second
multiplier 14 and is multiplied by the carrier output from a
carrier-generator 15, and then, the thus obtained output is
transmitted via an antenna 16. The carrier has the center frequency
f.sub.0 of 2.484 MHz, as mentioned above. In the embodiment shown
in FIG. 2, the baseband data is multiplied by the spread code and
the carrier in turn, but the multiplying turn may be reversed. That
is, the baseband data may be multiplied by the carrier and the
spread code in turn. Mathematically, the multiplication give the
same result irrespective of the multiplying turn. However, since
many circuits to treat 2.4 GHz band-signals are required in a
transmitter if the baseband data is multiplied by the carrier
firstly, it is difficult to shield high frequency signals
disadvantageously.
FIG. 4 shows diagrammatically a code division multiple
communication signal from the base stations 2a or 2b. As mentioned
above, the preamble division has 10-repeated synchronization
bursts, each being composed of the synchronization packet division
and the data division. Since in the data division, the baseband
data is modulated in spread spectrum by the orthogonal m-sequential
code of 64 chips, one data packet includes code division multiple
access signals of 500 symbols corresponding to 63 channels of
channel 1 to channel 63. FIG. 4 shows diagrammatically that the
preamble divisions are transmitted to the 63 channels in common. As
mentioned above, the period of the synchronization burst in the
preamble division (T.sub.burst) is the same as the period of the
symbol in the data division (T.sub.symbol)
FIG. 5 shows a construction of mobile stations (receiving stations)
4a, 4b In the conventional code division multiple access
communication system in the above Kokai Publication 9-261121(JP A
09-261121), the mobile station detected the carrier included in the
correlation peak from the surface acoustic wave-matched filter (SAW
MF) and generated the carrier synchronized with the carrier of the
received signal. Then, the combined signal of the generated carrier
and the synchronization code sequence was multiplied by the
received signal to reproduce the original baseband data. Since the
correlation peak from the surface acoustic wave matched filter (SAW
MF) has a short period of 500 nsec, it is actually very difficult
to reproduce the carrier from the received signal precisely in the
short period. This invention does not require to reproduce the
carrier from the received signal.
The mobile station branches the code division multiple signal
received at an antenna 21 by a branching filter 22, and one of the
branched signals is supplied to a gain-variable amplifier 23. A
level detector 24 detects, when the signal branched by the
branching filter 22 is received, the electric power level of the
received signal. A controlling signal generator 25 generates, when
the output signal of the level detector 24 is received, a
controlling signal, which is supplied to the amplifier 23 as a gain
controlling signal. These circuits constitutes an automatic gain
controlling circuit, and the amplifier 23 output a signal of a
given level constantly. In FIG. 5, the received signal is directly
input into the level detector, but the signal from the rear end of
the SAW MF, that is, from between the SAW MF 26 and the enveloped
cymoscope 27 is directly input into the level detector. Herein, the
level detector 24, the controlling signal generator 25 and the
gain-variable amplifier 23 may not be provided, depending on the
use of the code division multiple access communication system.
However, it may trouble the signal treatment after the enveloped
cymoscope 27.
The output signal from the amplifier 23 is supplied to the surface
acoustic wave-matched filter (SAW MF) 26, and the synchronization
code sequence in the preamble division is detected. Since the
surface acoustic wave-matched filter 26 is well known, the
explanation for the filter 26 is omitted. The SAW MF is described
in Kokai Publication 9-261121(JP A 09-261121).
Moreover, in H. Nakase, T. Kasai, Y. Nakamura, K. Masu and K.
Tsubouchi, "One Chip Demodulator Using RF Front-End SAW Correlator
for 2.4 GHz Asynchronous Spread Spectrum Modem", The 5th
International Symposium on Personal Indoor and Mobile Radio
Communications (PIMRC'94), The Hague, 374-378 (1994), the SAW MF
having an aluminum nitride/sapphire-structure, which is usable for
this invention, is described. The SAW MF having the aluminum
nitride/sapphire-structure operates at high acoustic wave velocity,
and has zero temperature coefficient-propagation delay time
characteristic. The line & space of the IDT (Inter Digital
Transducer) electrode in the SAW MF having an operation center
frequency of 2.4 GHz is set to 0.6 .mu.m, and can be fabricated
easily by a present microfabrication technique. If the SAW MF
having the center frequency of 2:4 GHz is made of another material,
the line & space of the IDT is set to 0.20.3 .mu.m, and have
difficulty in being fabricated by the microfabrication technique.
The surface acoustic wave matched filter, which outputs the
correlation peak from the directly inputting spectrum spread signal
of 2.4 GHz band, has preferably the aluminum
nitride/sapphire-structure, but it may have another structure. Not
considering the electric power consumption of the receiver, the
matched filter based on a Si ULSI technique may be employed.
When the surface acoustic wave matched filter 26 detects the
synchronization code sequence, it outputs the correlation peak.
Then, the correlation peak is supplied to the enveloped cymoscope
27, and the thus obtained output is supplied to the orthogonal code
synchronization circuit 28. The thus obtained output is supplied to
the orthogonal code-generating circuit 29 to generate the
orthogonal code synchronized with the synchronization code
sequence, that is, the orthogonal code with the chip
synchronization.
In the embodiment shown in FIG. 5, the detection of the correlation
peak is performed by the enveloped cymoscope, but may be done by
another method only if the method can detect the generation timing
of the correlation peak. In brief, the generation timing of the
correlation peak has only to be detected. A delay demodulation
circuit may be employed, although the use of the circuit
complicates the construction of the synchronization code sequence
and makes the construction of the receiver complex to some
degree.
In this embodiment, the orthogonal code generated, as mentioned
above, in the orthogonal code-generating circuit 29 is supplied to
a first multiplier 30, and is multiplied by the spectrum spread
signal branched at the branching filter 22. As a result, the
narrow-band modulation signal can be obtained.
FIG. 6A shows schematically the spectrum spread signal which is
supplied to the first multiplier 30, and FIG. 6B shows
schematically the narrow-band modulation signal output from the
first multiplier 30. Herein, the baseband data, the carrier, the
orthogonal code and the spectrum spread signal are represented by
"D(t)", "cos .omega.t", "C(t)" and "D(t).multidot.C(t)cos .omega.t,
respectively.
Generally, when the baseband data is modulated in BPSK (Bi-Phase
Shift Keying), the D(t) is set to "1" and "-1" at the baseband
data=1 and -1, respectively. Moreover, the secondary modulation to
multiple the orthogonal code is performed by a PSK modulation, the
C(t) is set to "1" and "-1" at the orthogonal code=1 and 0,
respectively. For example, when the code sequence of 11 chips is
set to .left brkt-top.11100010010.right brkt-bot., the C(t) is set
to .left brkt-top.+1,+1,+1,-1,-1,-1,+1,-1,-1,+1,-1.right brkt-bot..
When the carrier frequency is set to f.sub.0, the equation
.omega.2.pi.f.sub.0 is satisfied. The spectrum of
"D(t).multidot.C(t)cos .omega.t has a central wave having a two
times as large band width as the chip rate at the carrier center
frequency f.sub.0 and sideband waves at both sides of the central
wave. When the spectrum spread signal is transmitted under the rule
of RCR-STD 33, the electric power spectrum is repressed so that the
sideband wave can satisfy the rule. By multiplying the spectrum
spread signal and the orthogonal code with the chip
synchronization, the signal of D(t)cos .omega.t can be obtained.
The signal is a narrow-band modulation signal, and has a center
frequency equal to the carrier center frequency f.sub.0 and a small
band width of about 500 kHz.
In this embodiment, the thus obtained narrow-band modulation signal
is supplied to a second multiplier 31, and is multiplied by the
carrier having a frequency of 2.484 GHz which is generated from a
carrier generator 32, to be demodulated. The thus obtained output
is passed through a low path filter 33, and the baseband data can
be reproduced. The technique to demodulate the above narrow-band
modulation signal is well known, and by generating the carrier
synchronized with that of the received signal at the carrier
generator 32 by a method according to the technique, the baseband
data can be demodulated.
Herein, the concrete numerical value of the data rate of the down
link in this invention is exemplified. The number of the
synchronization burst in the preamble division is set to 10, and
the chip rate R.sub.pre of the synchronization packet division
(synchronization code sequence) in the synchronization burst is set
to 1 chip-Barker code of 22 Mcps. Then, the orthogonal code in the
data division is composed of the orthogonal m-sequential code of 64
chips, and the chip rate of the orthogonal code in the data
division (R.sub.data) is set to 1 Mcps. In this case, the period of
the symbol in the data division (T.sub.symbol) is set to (1/11
Mcps).times.64=5.8 .mu.sec. The number of the symbol in the data is
set to 500. The total sum of the preamble division and the data
division, that is, the packet length is set to
510.times.T.sub.symbol =2.96 .mu.sec. Since the data of 500 symbols
are transmitted per one packet, the real data rate per one packet
is (500/2.96 msec)=168 kbps. This data rate corresponds to that of
an incontinent transmission of packet. In the transmission and the
reception using TDD (Time division Duplex) at the up link and down
link, if the periods of the transmission and the reception in the
up link and the down link are divided equally, respectively, the
real data rate at the down link is set to 84 kbps, half of the
above real data rate of 168 kbps. It has to be emphasized that the
channel number is 64 and the data rate of each data rate is 64
kbps.
FIG. 7 is a block diagram showing another mobile station usable for
the code division multiple communication system of the present
invention. The same reference is given to the same part in FIG. 7
as the one in FIG. 5. In the above embodiment, the carrier
generator 32 generates the carrier having the same frequency as the
carrier of the received signal, that is, the carrier having the
center frequency of 2.484 GHz. In this embodiment, however, a
carrier generator 41, which generates a carrier having a different
frequency from the carrier frequency of the received signal, is
provided. Then, by multiplying the generated carrier and the above
narrow-band modulation signal with the second multiplier 31, the
narrow-band modulation signal, having the center frequency equal to
the differential frequency between their carrier frequencies, is
obtained. Lastly, the obtained narrow-band modulation signal is
detected by a detecting circuit 42 to demodulate the baseband data.
This modulation system is called as a "Heterodyne system". Since
the Heterodyne system is well known, the detail explanation is
omitted.
FIG. 8 is a block diagram showing a still another mobile station
usable for the code division multiple access communication system
of the present invention. In this embodiment, the same reference is
given to the same part. As mentioned in Kokai Publication
9-261121(JP A 09-261121), the carrier included in the correlation
peak from the surface acoustic matched filter 26 is detected and
reproduced, and the combined signal of the reproduced carrier and
the orthogonal code is multiplied by the spectrum spread signal to
demodulate the original baseband data.
That is, the signal including the correlation peak output from the
surface acoustic wave matched filter 26 is supplied to a carrier
generator 51. As shown in FIG. 9A, the signal including the
correlation peak has an extremely large amplitude when the
correlation peak is detected, but it has extremely small amplitude
at the time except the detection of the correlation peak.
Therefore, in the carrier generator 51, the signal including the
correlation peak is amplified with a limiter amplifier at the time
of and except the detection of the correlation peak, as shown in
FIG. 9B, and the gain thereof is controlled. Thereafter, the signal
is passed through a bandpass filter having a bandpass of 2.484 GHz,
and thereby, the carrier having a center frequency of 2.484 GHz is
generated. Besides the above construction, the carrier generator 51
may have another construction only if the generator 51 can
reproduce the carrier of the received signal. However, since the
correlation peak has an extremely short period of about 45 nsec in
the above embodiment, for downsizing the circuit and operating
stably, it is preferable that the signal including the correlation
peak is converted to a narrow-band modulation wave, and thereafter,
the converted modulation wave is demodulated in narrow-band.
The thus generated carrier is combined with the orthogonal code
with the chip synchronization generated in the orthogonal
code-generator 29 at a first multiplier 52. The combined signal is
multiplied by the code division multiple access signal received at
a second multiplier 53, and the output signal is supplied to a
integrator 54 to demodulate the original baseband data.
Although the present invention was described in detail with
reference to the above examples, this invention is not limited to
the above disclosure and every kind of variation and modification
may be made without departing from the scope of the present
invention. For example, it is apparent that the numerical values in
the above embodiments are exemplified and this invention is not
limited to the numerical values. For example, in the receiver shown
in FIGS. 5 and 7, the signal from the antenna, that is, the signal
having the center frequency of about 2.4 GHz is introduced into the
SAW MF via the branching filter and the amplifier. Since the
receiver does not require the down converting, advantageously, the
whole circuit can be easily fabricated. In the embodiments shown in
FIGS. 5 and 7, since the SAW MF including an aluminum nitride film
as its component can detect directly from the spectrum-spread
signal of 2.4 GHz, the above receiver can be realized. If the
signal from the antenna is multiplied by a sine wave signal having
a given frequency, the center frequency of the thus obtained signal
being down-converted, and is treated by the same manner as in the
embodiments shown in FIGS. 5 and 7, the same effect as in the above
embodiments can be obtained. In this case, the circuit for the down
converting is required. In employing the down-converted signal, it
is required that the center frequency of the SAW MF coincide with
the carrier frequency of the down-converted signal.
Moreover, in the above embodiments, the synchronization code
sequence in the preamble division is composed of the Barker code of
11 chips, and the orthogonal code in the data division is composed
of the orthogonal m-sequential code of 64 chips. However, the
synchronization code sequence in the preamble division and the
orthogonal code in the data division may be composed of a
m-sequential code of 15-chip m-sequential code and the orthogonal
m-sequential code, respectively. Moreover, the synchronization code
sequence in the preamble division and the orthogonal code in the
data division may be composed of the Barker code of 11 chips and
the orthogonal Walsh code, respectively. Then, the synchronization
code sequence in the preamble division and the orthogonal code in
the data division may be composed of the m-sequential code and the
orthogonal Walsh code, respectively. Furthermore, the orthogonal
code may be composed of the orthogonal Gold code.
In the above embodiments, although the preamble division has the
plural synchronization code sequence, it may have only one
synchronization code sequence if the period of the synchronization
burst in the preamble division is set equally to be the period of
the symbol in the data division.
Moreover, although in the above embodiments, each synchronization
code sequence constituting the plural synchronization bursts in the
preamble division has the same construction, it may have different
construction one another. In this case, plural surface acoustic
wave matched filters, each having different construction, are
employed for identifying the plural synchronization code sequences
having different constructions. Then, if the correlation peak of
one from among the plural synchronization code sequences is
detected by one of the plural surface acoustic wave matched
filters, the orthogonal code can be generated at the start timing
of the data division. By employing the plural synchronization code
sequences, each having different construction, the chip
synchronization can be attained precisely at a high speed under
various environment.
Moreover, although in the above embodiments in which the preamble
division has the plural synchronization burst, each synchronization
burst has only one synchronization code sequence, it may have
plural synchronization code sequences. In this case, the plural
synchronization code sequences may have the same construction or a
different constructions.
As mentioned above, according to the code division multiple access
communication system of the present invention in which the preamble
division has the plural synchronization code sequences, the chip
synchronization can be attained by detecting the correlation peak
of one from among the plural synchronization code sequences.
Therefore, the chip synchronization can be attained precisely at a
high speed under a bad environment, and the dropout of the whole
packet can be prevented extensively.
Furthermore, according to the code division multiple access of the
synchronization burst including the synchronization code sequence
in the preamble division is set to be integral times as long as
particularly equal to, the period of the symbol in the data
division, since the orthogonal code can be generated in accordance
with the start timing of the symbol in the data division by
detecting the correlation peak of one from among the plural
synchronization code sequences in the preamble division, the chip
synchronization can be attained precisely.
Moreover, according to the code division multiple access
communication system of the present invention in which the baseband
data is demodulated on the carrier generated in the mobile station
independently, since it is not required that the carrier is
generated from the received signal at the antenna, the baseband
data can be demodulated precisely.
* * * * *